System and method for transferring a session between multiple clients

ABSTRACT

A method for transferring a session between clients is provided when one user uses multiple clients on a service (for example, Push to talk over Cellular (PoC), Instant Messaging (IM), Converged-Internet Protocol (IP) Messaging (CPM)) providing system implemented through a Session Initiation Protocol (SIP)/IP core network. A session transfer method is provided when the user needs to transfer a session to another client while the session is performed through one client. A temporary storing technique is used in which a conversation server or client as one of elements of a seamless CPM system for providing a seamless user environment temporarily stores data transmitted from another user during session transfer.

PRIORITY

This continuation application claims priority under 35 U.S.C. §120 toU.S. patent application Ser. No. 12/990,749 (now in condition forallowance), which was a national stage application under 35 U.S.C. 371of Int'l Stage PCT Application Ser. No. PCT/KR2009/002212, filed on Apr.28, 2009, and which claimed priority under 35 U.S.C. 119(a) to KoreanPatent Application Ser. No. 10-2008-0041340, filed on May 2, 2008, theentire disclosures of each of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a service providing methodand system implemented through a Session Initiation Protocol/InternetProtocol (SIP/IP) core network, and in particular, to a method andsystem for transferring a session between multiple clients.

2. Description of the Related Art

In an existing mobile environment, terminals transmit sporadic messagesof Short Message Service (SMS), Multimedia Messaging Service (MMS), etc.On the other hand, users, may need a messaging service to easilyexchange a conversation using an MSN messenger in a wired environment.Thus, an instant messaging service has been introduced into terminalsand networks on the basis of an SIP/IP core network. According to thedemand of customers and enterprises for Push To Talk (PTT) (that is,walkie-talkie), a PTT over Cellular (PoC) service and system based onthe SIP/IP core network have been developed. According to rapidvariation of markets for enterprises, communication businesses, etc.,the desire of users to integrate and process various types of messagesis increasing. In consideration of this point, a standard technology isbeing developed for service Converged IP Messaging (CPM) implementedthrough the SIP/IP core network in the standard organization called OpenMobile Alliance (OMA). The CPM is intended to allow a user to experiencea seamless messaging service environment by integrating IP-basedmessaging services. Accordingly, the implementation of interworkingbetween a CPM service and a non-CPM service is needed such that aservice disconnection is not perceived in any messaging service. One ofmany features of the above-described CPM service is that multi-clientenvironments can be provided to users.

There is the case where the user needs to transfer a session to anotherclient while the session is performed through one client even when oneuser accesses a service by simultaneously using multiple clients throughthe above-described method. In this case, a proper session transfermethod and system are needed.

Accordingly, a method and system that can transfer a session in amessaging service providing system implemented through an SIP/IP corenetwork are needed.

SUMMARY OF THE INVENTION

The present invention addresses at least the problems and disadvantagesdescribed above and provides at least the advantages described below.

An aspect of the present invention is to address at least the problemsand/or disadvantages and to provide at least the advantages describedbelow. Accordingly, an aspect of the present invention is to provide amethod and system for transferring a session from one client to anotherclient when one user uses multiple clients.

According to an aspect of the present invention, there is provided aconverged messaging service providing system for transferring a sessionbetween multiple clients, including: a first client that requestssession transfer to a second client; a message & media storage thatstores a session history; and a conversation server that temporarilystores a message from a third client of another user when the sessiontransfer request exists, acquires a session history from the message &media storage, generates a session with the second client, and transmitsthe temporarily stored message and the session history to the secondclient when the session is generated completely.

According to an aspect of the present invention, there is provided aconverged messaging service providing system for transferring a sessionbetween multiple clients, including: a first client that requestssession transfer to a second client; a message & media storage thatstores a session history; a conversation server that temporarily storesa message from a third client of another user when the session transferrequest exists, generates a session with the second client, and commandsto generate a session between the second client and the message & mediastorage after transmitting the temporarily stored message to the secondclient when the session is generated completely; and the second clientthat generates a session with the message & media storage in response tothe session generation command and acquires a session history from themessage & media storage.

According to an aspect of the present invention, there is provided amethod for transferring a session between multiple clients in aconverged messaging service providing system, including: requestingsession transfer from a first client to a second client; temporarilystoring, by a converged server, a message from a third client when thesession transfer request exists; acquiring, by the converged server, asession history from a message & media storage; generating, by theconverged server, a session with the second client; and transmitting, bythe converged server, the temporarily stored message and the sessionhistory to the second client when the session is generated completely.

According to an aspect of the present invention, there is provided amethod for transferring a session between multiple clients in aconverged messaging service providing system, including: requestingsession transfer from a first client to a second client; temporarilystoring, by a converged server, a message from a third client when thesession transfer request exists; generating, by the converged server, asession with the second client; transmitting, by the converged server,the temporarily stored message to the second client when the session isgenerated completely; acquiring, by the converged server, a sessionhistory from a message & media storage; and transmitting, by theconverged server, the session history to the second client.

According to an aspect of the present invention, there is provided amethod for transferring a session between multiple clients in aconverged messaging service providing system, including: requestingsession transfer from a first client to a second client; temporarilystoring, by a converged server, a message from a third client when thesession transfer request exists; generating, by the converged server, asession with the second client and transmitting the temporarily storedmessage to the second client when the session is generated completely;commanding, by the converged server, to generate a session between thesecond client and a message & media storage; generating, by the secondclient, a session with the message & media storage in response to thesession generation command; and acquiring, by the second client, asession history from the message & media storage.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a configuration diagram of a CPM system according to anembodiment of the present invention;

FIG. 2 illustrates an operation relation between CPM system elements fortransferring a session according to an embodiment of the presentinvention;

FIG. 3 illustrates a session transfer flow according to a firstembodiment of the present invention;

FIG. 4 is a state diagram of client #A-1 according to the firstembodiment of the present invention;

FIG. 5 is a state diagram of client #A-2 according to the firstembodiment of the present invention;

FIG. 6 is a state diagram of a conversation server according to thefirst embodiment of the present invention;

FIG. 7 is a state diagram of a message & media storage according to thefirst embodiment of the present invention;

FIG. 8 illustrates a session transfer flow according to a secondembodiment of the present invention;

FIG. 9 is a state diagram of client #A-2 according to the secondembodiment of the present invention;

FIG. 10 is a state diagram of a conversation server according to thesecond embodiment of the present invention;

FIG. 11 illustrates a session transfer flow according to a thirdembodiment of the present invention;

FIG. 12 is a state diagram of a client #A-2 according to the thirdembodiment of the present invention;

FIG. 13 is a state diagram of a conversation server according to thethird embodiment of the present invention;

FIG. 14 is a state diagram of a message & media storage according to thethird embodiment of the present invention; and

FIG. 15 illustrates an SIP REFER message format according to anembodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings. In the drawings, the same or similarelements are denoted by the same reference numerals even though they aredepicted in different drawings. In the following description, a detaileddescription of known functions and configurations incorporated hereinhas been omitted for clarity and conciseness.

According to embodiments of the present invention, session transfer isnaturally performed without lost content by temporarily storing andtransmitting a session history and a message of a counterpart user to asecond client during the session transfer. In a target client to whichthe session has been transferred, a session history of an existingclient is output to a screen, such that a user can continue aconversation while referring to existing conversation content. The userdoes not need to read conversation content from the screen of theprevious client. User convenience can be improved using a CPM service.

In the present invention, an example of CPM messaging among messagingservices implemented through an SIP/IP core network will be described.The present invention provides a method for transferring a sessionbetween clients when one user uses multiple clients on a service (forexample, PoC, Instant Messaging (IM), or CPM) providing systemimplemented through an SIP/IP core network. In particular, the presentinvention provides a session transfer method when the user needs totransfer a session to another client while the session is performedthrough one client. The present invention uses a temporary storingtechnique in which a conversation server or client as one of elements ofa seamless CPM system for providing a seamless user environmenttemporarily stores data transmitted from another user while the sessionis transferred.

Hereinafter, the configuration and operation of the CPM system accordingto an embodiment of the present invention will be described withreference to FIG. 1. In the embodiment of the present invention, anexample of the CPM will be described, but the present invention isapplicable to all services implemented through the SIP/IP core networksuch as PoC, IM, etc. For the session transfer according to theembodiment of the present invention, the CPM system includes aconversation server and a message & media storage. Specifically,referring to FIG. 1, the CPM system includes a CPM client 200, a CPMconversation server 210, a message & media storage 220, a CPM userpreference entity 230, an interworking function entity 240, and anotification entity 250.

First, the CPM client 200 is a service requestor to generate a sessionwith another CPM client through the CPM conversation server 210 andreceive a service. The message & media storage 220 stores data to beexchanged in a session between the CPM clients. An operation for storingCPM session data is determined by user preferences stored in the CPMuser preference entity 230. The constituent elements are mutuallyconnected through interfaces. Among the interfaces, an interface betweenthe CPM conversation server 210 and the CPM client 200 uses SIP, MessageSession Relay Protocol (MSRP), and Real-time Transfer Protocol (RTP) asCPM-CONV.

The operation relation between the CPM system elements will be describedwith reference to FIG. 2. One user can use multiple clients. In FIG. 2,when a user A uses first and second clients and a user B uses a thirdclient, a session transfer method between the first and second clientsis proposed. Specifically, FIG. 2 schematically illustrates a process inwhich the user A attempts a client change to a client #A-2 1100 while aclient #A-1 1000 exchanges data with a client #B 2000. In the presentinvention, the session transfer method is implemented such that the userB does not know the fact that the user A has made the client change. Inthe present invention, the session transfer is that in a messagingsession and an additionally continuous media session. Here, the messagesession is the session for exchanging a message, file, photo, etc.between users. That is, it can be defined as a discontinuous mediasession. A concept as opposed thereto is a continuous media session likea video conferencing session or a voice chatting session for a voiceconversation.

In the following description, it is assumed that the user A owns theclient #A-1 1000 and the client #A-2 1100 and the user B owns the client#B 2000. Here, the client #A-1 1000 and the client #B 2000 are connectedto a conversation server 3000 by the SIP session. The conversationserver 3000 and a message & media storage 4000 use Internet MessageAccess Protocol 4 (IMAP4)/Lemonade protocol, such that theIMAP4/Lemonade protocol is used for message exchange with the message &media storage 4000. In the present invention, the message & mediastorage 4000 is additionally required to store a session history.

On the other hand, when the user A desires to attempt the client changeto the client #A-2 1100, the client #A-1 1000 as a source devicerequests the conversation server 3000 to transfer the session. At thistime, the client #A-1 1000 has its own client list and selects one ofclients belonging to the user. For example, the client #A-1 1000 mustrequest the conversation server 3000 to transfer the session afterselecting the client #A-2 1100.

Upon receipt of a session transfer command, the conversation server 3000temporarily stores data transmitted from the client #B 2000 andtransmits the stored data to the client #A-2 1100 when the sessiontransfer process is completed. At this time, a session history is storedin the message & media storage 4000. The client #A-2 1100 acquires thesession history stored in the message & media storage 4000 through theconversation server 3000 or by directly accessing the message & mediastorage 4000. A session history transmission time and method aredetermined by the CPM user preference and service policy. Here, thesession history is defined as a set of all types of data exchanged froma session start time to a current time. This session history can bemanaged by the message & media storage 4000 according to the CPM userpreference and service policy or directly managed by the client #A-11000 as the originator device.

The embodiments herein are divided as follows.

A first embodiment of the present invention is a process in which theconversation server 3000 receives and temporarily stores a sessionhistory from the message & media storage 4000 when a session transfercommand is generated and transmits the session history and a temporarilystored message to the client #A-2 1100 after the session with the client#A-2 1000 is generated, and the client #A-2 1100 outputs a transmissioncompletion notification to a screen when the transmission is completedand resumes a conversation with the client #B 2000.

A second embodiment of the present invention is a process in which theconversation server 3000 temporarily stores a message to be transmittedto the client #A-2 1100 while a session with the client #A-2 1100 isgenerated, the temporarily stored message is transmitted to the client#A-2 1100 when the session is generated, the conversation is resumedbetween the client #A-2 1100 and the client #B 2000 when thetransmission is completed, the conversation server 3000 requests themessage & media storage 4000 to transmit a session history and receivesand temporarily stores the session history, the session history istransmitted to the client #A-2 1100, and the session history is outputto the screen of the client #A-2 1100.

A third embodiment of the present invention is the same as the secondembodiment in terms of the process until a conversation is resumedbetween the client #A-2 1100 and the client #B 2000. In a subsequentprocess of the third embodiment, the conversation server 3000 commandsthe client #A-2 1100 to generate a session with the message & mediastorage 4000, and the client #A-2 1100 directly receives a sessionhistory through the generated session and outputs the received sessionhistory to the screen.

First, a session transfer flow according to the first embodiment of thepresent invention will be described with reference to FIG. 3.

Referring to FIG. 3, the client #A-1 1000 transmits a request fortransferring a session to the client #A-2 1100 to the conversationserver 3000 using an SIP REFER message as a control message (S101). Theformat of the SIP REFER message is illustrated in FIG. 15. Referring toFIG. 15, a Refer-To header field P1 indicates destination addressinformation. To transfer the session from the client #A-1 1000 to theclient #A-2 1100, an SIP URI address of the client #A-2 1100 isindicated. The REFER message includes attribute information indicatingthat the REFER message to be currently transmitted is used for thesession transfer. Accordingly, SESSION TRANSFER P2 is indicated by aSession Description Protocol (SDP) attribute parameter. Upon acquisitionof the REFER message, the conversation server 3000 uses an ACCEPTEDmessage to indicate whether the REFER message has been received (S102).To notify that a REFER event occurs in the conversation server 3000, theconversation server 3000 transmits a NOTIFY message to the client #A-11000 (S103). The client #A-1 1000 returns an OK message in response tothe NOTIFY message (S104). The above-described steps S101 to S104indicated by reference numeral 300 are a process in which the client#A-1 1000 requests the conversation server 3000 to transfer the session.

Then, the conversation server 3000 performs the following sessiontransfer procedure. Specifically, when the session transfer isperformed, the conversation server 3000 temporarily stores data, forexample, messages 305, to be transmitted from the user B to the user A.In other words, during the session transfer, a temporary storingoperation 310 is started such that data from the user B to the user A istransmitted to the client #A-2 1100 of the user A without loss.

The conversation server 3000 selects a storage space of the user Awithin the message & media storage 4000 using an IMAP SELECT message(S105). At this time, the conversation server 3000 uses an IMAP protocolto acquire a session history stored in the message & media storage 4000.Then, the message & media storage 4000 returns an OK FETCH message inresponse to the storage space selection by the conversation server 3000(S106). Subsequently, the conversation server 3000 transmits an IMAPFETCH message to retrieve the session history stored in the message &media storage 4000 (S107). The message & media storage 4000 transmitsthe session history to the conversation server 3000 and the conversationserver 3000 temporarily stores the session history in its own storagespace (S108). The above-described steps S105 to S108 indicated byreference numeral 315 are a process in which the conversation server3000 retrieves and receives the session history from the message & mediastorage 4000.

Subsequently, the conversation server 3000 makes a notification of anewly generated session with the client #A-2 1100 using an INVITEmessage (S109). The client #A-2 1100 returns an OK message in responseto the INVITE message (S110). Then, the conversation server 3000 returnsan ACK message in response to the OK message (S111). The above-describedsteps S109 to S111 indicated by reference numeral 320 are a new SIPsession generation process.

When the session with the client #A-2 1100 is generated completely, arouting change 325 is made such that the conversation server 3000connects the conversation with the user B to the client #A-2 1100. Thatis, routing setup is changed to transmit data from the client #B 2000 tothe client #A-2 1100. At a routing change point, the conversation server3000 terminates an operation for temporarily storing data received fromthe client #B 2000 as indicated by reference numeral 330.

Then, the conversation server 3000 notifies the client #A-1 1100 ofREFER event termination using a NOTIFY message (S112). The client #A-11000 returns an OK message to the conversation sever 3000 in response tothe NOTIFY message (S113). The client #A-1 1000 notifies theconversation sever 3000 of existing session termination (S114). Theconversation server 3000 transmits the OK message to confirm the sessiontermination (S115). Accordingly, the session with the client #A-1 1100is terminated through steps S112 to S115 indicated by reference numeral335.

Then, the conversation server 3000 transmits a session history and atemporarily stored message to the client #A-2 1100 using the MSRPprotocol (S116 and S117). In response thereto, the client #A-2 1100returns an OK message to the conversation server 3000 (S118 and S120).When the session history and the temporarily stored message aretransmitted completely, the client #A-2 1100 notifies the conversationserver 3000 of transmission completion using an MSRP REPORT message(S119 and S121). Through the above-described steps S116 to S121, theclient #A-2 1100 outputs the temporarily stored message and the sessionhistory received from the conversation server 3000 to the screen.Accordingly, the conversation server 3000 receives data, for example,messages, from the user B to the user A, such that the conversation withthe client #B 2000 is continued.

Hereinafter, the operation of constituent elements of the CPM systemoperating as illustrated in FIG. 3 will be described with reference toFIGS. 4 to 7.

FIG. 4 illustrates the state variation of the client #A-1 1000 accordingto the first embodiment of the present invention. When the client #A-11000 of an initial state in step 400 requests the conversation server3000 to transfer a session in step 402, the transition to an idle stateis made in step 404. Then, when a termination command to terminate anexisting session is received from the conversation server 3000 in step406, the transition to a termination state is made in step 408.

FIG. 5 illustrates the state variation of the client #A-2 1100. When theclient #A-2 1100 of an initial state in step 410 receives a temporarilystored message and a session history from the conversation server 3000in step 412, the session history and the temporarily stored message arerendered in steps 414 and 416. Subsequently, when the conversation withthe client #B 2000 is resumed in step 418, the transition to aconversation resumption state is made in step 420.

FIG. 6 illustrates the state variation of the conversation server 3000.When the conversation server 3000 of an initial state in step 422receives a session transfer command from the client #A-1 1000 in step424, a temporary storing operation is started in step 426. Subsequently,when a storage space of the message & media storage 4000 is selected instep 428, an operation is performed in a selection state in step 430.When a session history retrieval operation must be performed in themessage & media storage 4000 in step 432, a session history is retrievedin step 434. Accordingly, when the session history within the message &media storage 4000 is received in step 436, an operation is performed ina session history reception state to receive the session history in step438. Then, when the session with the client #A-2 1100 is generated instep 440, an operation for inviting the client #A-2 1100 is performed instep 442. Then, when a routing change to the client #A-2 1100 is made instep 444, the conversation server 300 performs a temporary storingoperation in step 446. Thereafter, when the temporarily stored messageand the session history must be transmitted to the client #A-2 1100 instep 448, an operation is performed in a state for transmitting thetemporarily stored message and the session history in step 450. Then,when the transmission is completed in step 452, the conversation server3000 operates in an idle state in step 454.

FIG. 7 illustrates the state variation of the message & media storage4000. When the message & media storage 4000 is in an initial state instep 456 and a storage space within the message & media storage 4000 isselected in step 458, it proceeds to step 460 to perform an operation ina selection state. Subsequently, when a session history is retrievedfrom the message & media storage 4000 in step 462, an operation isperformed in a session history retrieval state in step 464. Then, whenthe message & media storage 4000 must transmit the retrieved sessionhistory to the conversation server 3000 in step 466, an operation fortransmitting the session history is performed in step 468. When thetransmission is completed in step 470, an operation is performed in anidle state in step 472.

In the case of source device initiated session transfer in which asession history is received in a foreground manner according to thefirst embodiment of the present invention as described above, a processfor outputting a session history and a temporarily stored message to thescreen of the client #A-2 1100 and resuming the conversation with theclient #B 2000 is performed. Accordingly, the present invention canminimize the inconvenience due to the session transfer since the user Acontinues the conversation through the client #A-2 1100, and can provideuser convenience since a waiting time of the user B due to the sessiontransfer of the user A is minimized.

Hereinafter, a session transfer flow according to the second embodimentof the present invention will be described with reference to FIG. 8. Theoperation of steps S201 to S204 of FIG. 8 as indicated by referencenumeral 500 is the same as that of steps S101 to S104 of FIG. 3. Anoperation 515 for temporarily storing a message 510 received from theclient #B 2000 is started. During this operation, the conversationserver 3000 performs an operation for generating a session with theclient #A-2 1100. The operation of steps S205 to S207 as indicated byreference numeral 520 is the same as that of steps S109 to S111 of FIG.3 as indicated by reference numeral 320. Since a routing changeoperation 525 and a temporary storage termination operation 530 are thesame as those as indicated by reference numerals 325 and 330 of FIG. 3,their description is omitted. Steps S208 to S211 as indicated byreference numeral 535 are the same as steps S112 to S115 of FIG. 3 asindicated by reference numeral 335.

In this regard, the process of FIG. 3 in which the conversation server3000 receives a session history from the message & media storage 4000and then transmits both a temporarily stored message and the sessionhistory to the client #A-2 1100 is performed, while the process of FIG.8 in which the conversation server 3000 first transmits the temporarilystored message to the client #A-2 1100 and then transmits the sessionhistory from the message & media storage 4000 to the client #A-2 1100 isperformed. As described above, when the client #A-2 1100 receives thetemporarily stored message from the conversation server 3000, themessage can be output to the screen, such that the conversation with theclient #B 2000 is continued.

Accordingly, when the conversation server 3000 transmits the temporarilystored message in steps S212 to S214 as indicated by reference numeral545, the session history is received from the message & media storage4000 in steps S215 to S218 as indicated by reference numeral 550. Here,the operation of steps S212 to S214 as indicated by reference numeral545 is the same as that of steps S116, S118, and S119 of FIG. 3, and theoperation of steps S215 to S218 as indicated by reference numeral 550 isthe same as that of steps S105 to S108 of FIG. 3 as indicated byreference numeral 315. An operation in which the conversation server3000 transmits the session history to the client #A-2 1100 in steps S219to S221 as indicated by reference numeral 555 is the same as that ofsteps S117, S120, and S121 of FIG. 3. When the session history isreceived, the client #A-2 1100 outputs the received session history tothe screen.

The operation of constituent elements of the CPM system operating asillustrated in FIG. 8 will be described with reference to FIGS. 9 and10. Since the state variation of the client #A-1 1000 requesting thesession transfer and the state variation of the message & media storage4000 are the same as those of FIGS. 4 and 7, their description isomitted.

FIG. 9 illustrates the state variation of the client #A-2 1100. When theclient #A-2 1100 of an initial state in step 600 receives a temporarilystored message from the conversation server 3000 in step 602, thetemporarily stored message is rendered in step 604. Subsequently, whenthe conversation with the client #B 2000 is resumed in step 606, thetransition to a conversation resumption state is made in step 608. Then,when the client #A-2 1100 receives a session history from theconversation server 3000 in step 610, the session history is rendered instep 612.

FIG. 10 illustrates the state variation of the conversation server 3000.When the conversation server 3000 of an initial state in step 614receives a session transfer command from the client #A-1 1000 in step616, a temporary storing operation is started in step 618. Afterpre-requesting the message & media storage 4000 to provide the sessionhistory in step 620, the conversation server 3000 invites the client#A-2 1100 in step 622. Then, when a routing change to the client #A-21100 is made in step 624, the conversation server 3000 performs atemporary storing operation in step 626. Subsequently, when a storagespace of the message & media storage 4000 is selected in step 628, theconversation server 3000 operates in a selection state in step 630. Whena session history retrieval operation must be performed in the message &media storage 4000 in step 632, a session history is retrieved in step634. Accordingly, when the session history within the message & mediastorage 4000 is received in step 636, an operation is performed in asession history reception state to receive the session history in step638. Then, when the temporarily stored message and the session historymust be transmitted to the client #A-2 1100 in step 640, the sessionhistory is transmitted in step 642. When the transmission is completedin step 644, an operation is performed in an idle state in step 646.

Hereinafter, a session transfer flow according to the third embodimentof the present invention will be described with reference to FIG. 11. Anoperation for transmitting the temporarily stored message in steps S301to S314 of FIG. 11 is the same as that of steps S201 to S214 of FIG. 8.In this regard, in FIG. 11, a process in which the client #A-2 directlyaccesses the message & media storage 4000 and directly acquires asession history without passing through the conversation server 3000 isperformed.

Accordingly, the client #A-2 1100 must newly generate a session with themessage & media storage 4000. The conversation server 3000 makes acommand for generating a session between the client #A-2 1100 and themessage & media storage 4000 using a REFER message (S315). Uponacquisition of the REFER message, the client #A-2 1100 uses an ACCEPTEDmessage to indicate whether the REFER message has been received (S316).To notify that a REFER event operates in the client #A-2 1100, theclient #A-2 1100 transmits a NOTIFY message to the conversation server3000 (S317). The conversation server 3000 returns an OK message inresponse to the NOTIFY message (S318).

Then, the client #A-2 1100 transmits an INVITE message to generate asession with the message & media storage 4000 (S319). The message &media storage 4000 returns an OK message in response to the INVITEmessage (S320). In response to the OK message, an ACK message isreturned to the message & media storage 4000 (S321). Accordingly, asession between the client #A-2 1100 and the message & media storage4000 is generated completely and the client #A-2 1100 can receive asession history through the session.

On the other hand, the client #A-2 1100 uses an IMAP protocol to acquirea session history stored in the message & media storage 4000. The client#A-2 1100 uses an IMAP LOGIN message for user login in the message &media storage 4000 (S322). The client #A-2 1100 receives an OK LOGINmessage from the message & media storage 4000 (S323). The client #A-21100 selects a storage space of the user A of the message & mediastorage 4000 using an IMAP SELECT message (S324). The message & mediastorage 4000 returns a response to the selection of the storage space ofthe client #A-2 1100 (S325). The client #A-2 1100 transmits an IMAPFETCH message to retrieve the session history stored in the message &media storage 4000 (S326). The message & media storage 4000 transmitsthe session history to the client #A-2 1100 (S327).

The client #A-2 1100 notifies the conversation server 3000 of REFEREVENT termination using a NOTIFY message (S328). The conversation server3000 returns a response to the NOTIFY message to the client #A-2 1100(S329).

The operation of constituent elements of the CPM system operating asillustrated in FIG. 11 will be described with reference to FIGS. 12 to14. Here, since the state variation of the client #A-1 1000 requestingthe session transfer is the same as that of FIG. 4, its description isomitted.

FIG. 12 illustrates the state variation of the client #A-2 1100. Whenthe client #A-2 1100 of an initial state in step 800 receives atemporarily stored message from the conversation server 3000 in step802, the temporarily stored message is rendered in step 804.Subsequently, when the conversation with the client #B 2000 is resumedin step 806, the transition to a conversation resumption state is madein step 808. Then, when a session with the message & media storage 4000is generated in step 810, an operation is performed in a sessiongeneration state in step 812, such that the session generation operationis completed. Subsequently, when the client #A-2 1100 logs in themessage & media storage 4000 in step 814, the transition to a loginstate is made in step 816. When a storage space of the message & mediastorage 4000 is selected in step 818, an operation is performed in aselection state in step 820. When a session history retrieval operationmust be performed in the message & media storage 4000 in step 822, theclient #A-2 1100 retrieves a session history in step 824. Accordingly,when the session history is transmitted from the message & media storage4000 in step 826, the session history is received in step 828. When ascreen output operation is performed in step 830, the received sessionhistory is output on the screen of the client #A-2 1100. Accordingly,the session history is rendered in step 832.

FIG. 13 illustrates the state variation of the conversation server 3000.When the conversation server 3000 of an initial state in step 834receives a session transfer command from the client #A-1 1000 in step836, a temporary storing operation is started in step 838. Afterpre-requesting the message & media storage 4000 to provide the sessionhistory in step 840, the conversation server 3000 invites the client#A-2 1100 in step 842. Then, when a routing change to the client #A-21100 is made in step 844, the conversation server 3000 performs atemporary storing operation in step 846. Subsequently, when theconversation server 3000 must transmit the temporarily stored message tothe client #A-2 1100 in step 848, the temporarily stored message istransmitted to the client #A-2 1100 in step 850. Subsequently, when themessage transmission is completed, the conversation server 3000determines that a session generation command is needed in step 852 andoperates in an idle state in step 856 after commanding the client #A-21100 to generate a session with the message & media storage 4000 in step854.

FIG. 14 illustrates the state variation of the message & media storage4000. When the message & media storage 4000 is in an initial state instep 858 and the client #A-2 1100 performs a login operation in step860, the message & media storage 4000 operates in a login state in step862. Subsequently, when a storage space of the message & media storage4000 is selected in step 864, the message & media storage 4000 operatesin a selection state in step 866. Subsequently, when a session historyis retrieved from the message & media storage 4000 in step 868, themessage & media storage 4000 operates in a session history retrievalstate in step 870. Then, when the session history must be transmitted tothe client #A-2 1100 in step 872, the message & media storage 4000performs an operation for transmitting the session history to the client#A-2 1100 in step 874. When the transmission is completed in step 876,the message & media storage 4000 operates in an idle state in step 878.

In the case of a source device initiated session transfer flow model inwhich a session history is transmitted in a background manner accordingto the second embodiment of the present invention and a source deviceinitiated session transfer flow model in which the client directlyreceives a session history from the message & media storage 4000according to the third embodiment of the present invention, a waitingtime of the user B can be minimized by minimizing a session transfertime with only a session generation time in the conversation server3000. Accordingly, after session history transmission is completedthrough session media transmission immediately after the user A performsthe session transfer, the session history can be referred to, such thatthe user A can refer to the session history during the conversation.

While the session transfer between multiple clients is in progress, forexample, while the session transfer is in progress when the user A makesa request for transferring the session to another client of the user A,the user B holding a conversation with the user A does not know thissituation. Thus, the session transfer according to the embodiment of thepresent invention can be referred to as transparency session transfer.For the transparency session transfer, it must be ensured that data fromthe user B to the user A safely arrives at the client #A-2 1100 withoutdata loss. In the present invention, the transparency session transferis ensured through the temporary storing technique.

Specifically, from the moment when the user A requests the sessiontransfer and sends its notification to the conversation server 3000, theconversation server 3000 intercepts and temporarily stores data, forexample, a message, transmitted from the user B. Subsequently, theconversation server 3000 must generate a session with the client #A-21100 and make a routing change. The temporary storing operation isterminated and the temporarily stored message is transmitted to theclient #A-2 1100. Thus, the message transmitted by the user B istransmitted to the user A in the temporarily stored message form withoutomission.

As is apparent from the foregoing description, according to embodimentsof the present invention, session transfer is naturally performedwithout lost content by temporarily storing and transmitting a sessionhistory and a message of a counterpart user to a second client duringthe session transfer. In a target client to which the session has beentransferred, a session history of an existing client is output to ascreen, such that a user can continue a conversation while referring toexisting conversation content. The user does not need to readconversation content from the screen of the previous client. Userconvenience can be improved using a CPM service.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. A conversation server for transferring a sessionbetween multiple clients, the server comprising: a storage thattemporarily stores a message from a third client of another user when afirst client requests session transfer to a second client; and acontroller that acquires a session history from a message and mediastorage, generates a session with the second client, and transmits thetemporarily stored message and the session history to the second clientwhen the session is generated completely.
 2. The conversation server ofclaim 1, wherein after transmitting the temporarily stored message tothe second client, the controller commands to generate a session betweenthe second client and the message and media storage.
 3. The conversationserver of claim 1, wherein after transmitting the temporarily storedmessage to the second client, the session history is acquired from themessage and media storage.
 4. The conversation server of claim 1,wherein after changing routing setup to the second client when thesession is generated completely, the controller terminates thetemporarily storing operation and terminates a session with the firstclient.
 5. The conversation server of claim 1, wherein Internet MessageAccess Protocol (IMAP) is used to acquire the session history.
 6. Theconversation server of claim 1, wherein the request for the sessiontransfer to the second client uses a Session Initiation Protocol (SIP)REFER message and the SIP REFER message comprises address information ofthe second client and attribute information indicating a message for thesession transfer.
 7. The conversation server of claim 2, wherein thesecond client that generates a session with the message and mediastorage in response to the session generation command and acquires asession history from the message and media storage.
 8. The conversationserver of claim 7, wherein the second client uses IMAP to acquire thesession history.
 9. A method for transferring a session between multipleclients in a service system implemented through an SIP/IP core network,the method comprising: temporarily storing, by a converged server, amessage from a third client when a first client requests sessiontransfer to a second client; acquiring a session history from a messageand media storage; generating a session with the second client; andtransmitting the temporarily stored message and session history to thesecond client when the session is generated completely.
 10. The methodof claim 9, wherein after transmitting the temporarily stored message tothe second client, the session history is acquired from the message andmedia storage.
 11. The method of claim 9, further comprising:terminating the temporary storing operation after changing routing setupto the second client when the session is generated completely; andterminating the session with the first client.
 12. The method of claim9, wherein Internet Message Access Protocol (IMAP) is used to acquirethe session history.
 13. The method of claim 9, further comprising:commanding to generate a session between the second client and themessage and media storage after transmitting the temporarily storedmessage to the second client.
 14. The method of claim 10, wherein thesecond client generates a session with the message and media storage inresponse to the session generation command and acquires the sessionhistory from the message and media storage.
 15. The method of claim 9,wherein the request for the session transfer to the second client uses aSession Initiation Protocol (SIP) REFER message and the SIP REFERmessage comprises address information of the second client and attributeinformation indicating a message for the session transfer.